h-bridgestepper motorstepper-driver
I know that stepper motors are usually driven with current-limiting chopper drivers and hence the applied voltage doesn't really matter (or does it?) and that's why specs of stepper motors don't state a max voltage but a max current instead.
However, I'd like to drive a Nema23 with a SparkFun Monster Moto Shield and an Arduino Uno.
This is the info I have about the motor
How do I calculate the DC voltage I can apply to the VMOT of the motor driver shield without frying the motor?
I would suggest driving the motor with 72% of rated current, or about 310mA. That should yield the same power dissipation as would be expected from unipolar drive at 440mA. When the motor isn't moving, the voltage would have to be about 31 volts. I wouldn't expect insulation problems at 31 volts, or even 50, but I don't know how far one could safely go. Perhaps measure the AC voltage when hand-spinning the motor quickly to see if there seems to be a limit.
Unless there is some nuance of the question I am missing:
A constant voltage (L/R type) stepper motor driver for a stepper motor is a pair of H-bridges, with no current limiting / chopping. It is not that these devices are no longer made, they are typically not sold as "stepper motor drivers".
For instance, the classic L298 (L298N, L298D) dual H-bridge IC will drive a bipolar stepper in constant voltage mode, thus:
simulate this circuit – Schematic created using CircuitLab
Eliminate the sense resistors, and there is no current limiting left - or preferably leave them there, and size them purely for failure conditions i.e. short circuit protection.
At 160 Ohms minimum coil resistance and a 35 Volt motor supply, the resultant maximum 219 mA per channel is easily handled by the L298's 2 Ampere per channel DC current rating.
The L298 in its various variants is still manufactured: Go with the L298D to take advantage of the integrated back-EMF protection diodes, given the inductive load.
While there are also MOSFET based H-bridge ICs available, offering greater efficiency, this may be irrelevant in a design where the efficiency loss in the series R added to each coil is likely to be the biggest heat contributor anyway.
About using a chopper driver as an L/R driver: The qualified answer is yes, as long as basic full-step driving is being attempted. It is only with micro-stepping that fine current control becomes a necessity.
Some chopper drivers may not like not receiving current feedback, and may flag a fault, but the typical full-step driver will not care, it will simply pass all current up to the resistance-limited value of the stepper (160 to 219 mA per channel, at given coil specifications), and not initiate chopping.
Best Answer
From the data sheet at Sparkfun for the motor shield, the absolute maximum voltage is 41 volts and the absolute maximum current is 30 amps. For normal operation, input voltage is 9-16 volts.